UntitledAcopper-aluminium connection is used for instance in an indus- trial estate where local business
use copper supply cables which are then fed off an aluminium ring main. But also in electrical substations it is necessary to connect aluminium con- ductors to copper bus bars. The main problem here is that connecting alu- minium and copper is not straight- forward. To ensure a safe and correct connection the use of special alu- minium/copper cable lugs and connec- tors are essential. (Picture 1).
Aluminium-Copper: A problematic connection
Generally aluminium is a reactive mate- rial that oxidizes easily, but in practice it has proved to offer good corrosion resistance. This characteristic is due to a chemical reaction that takes place when in contact with atmospheric oxy- gen resulting in a very thin but also
very resistant oxide layer being formed. (oxide barrier)
When metals are connected to those with a higher electrical potential such as copper in the presences of an elec- trolyte (condensed water) will result in an electrochemical reaction taking place. During this process the differ- ences caused in electrochemical poten- tial can have a significant impact.
An electrical circuit is generated by the copper electrode (anode), the elec- trolyte (water) and the aluminium elec- trode (cathode). The voltage generated in this copper and aluminium circuit “semi metallic” state results in a short circuit.
As a result of the current generated the Aluminium surface breaks down causing the metal to electrolytically decompose. This destructive process is visible as a kind of blooming oxidation and begins already with the existence of tiny copper particles on the alu- minium; this ongoing reaction itself does not cause the copper to corrode. In an electrical connection however the resistance is increased leading to increased temperatures which then in the worst case lead to a fire.
Therefore when connecting copper and aluminium it is important to ensure
that no moisture can enter the connec- tions. In an environment where mois- ture is present the contact points between the copper and aluminium need to be protected by using accurate operating procedures. (see picture 2). Primarily this requires the use of alu- minium/copper cable lugs and connec- tors. Due to the design of these lugs areas where moisture could accumu- late and where the oxidation process could start have been avoided. For this reason aluminium/copper cable lugs and connectors are specified for the use in off-shore wind power stations.
Aluminium/copper compression cable lugs
Leading manufacturers of high quality compression cable lugs for connecting aluminium connectors with copper bus bars (see picture 3) consist of an elec- trolytic aluminium (E-Al) compression and are joined to a copper palm (to EN 13600).
The available cross sections range from 16 mm2 up to 400 mm2. The field of application covers in principle all non-tension connections of aluminium cables acc. to DIN 48201, part 1, and aluminium ropes acc. to DIN 50182. Specifications and processing of alu-
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Copper due to its outstanding electrical properties are always the first choice when selecting a conductor for an electrical connection. A practicable alternative in many cases is aluminium particularly because of its low weight and easy application. In practice however the electrician can find it challenging to connect both these materials in a professional manner.
Accurately connecting copper and aluminium
Electroinstallation IN BRIEF Copper and Aluminium conductors are difficult to connect to each other. It is therefore necessary to avoid the ingress of moisture at all costs. For these applications special cable lugs are needed and accurate operating procedures should be adhered to.
Picture 1: Use of an incorrect crim- ping die and/or an incorrect crimp will result in an over compression (right) or an under compression (left) and in the worst case in fire.
Picture 2: The construction of Al/Cu cable lugs prevents any gaps which
would allow the accumulation of liquid to take place which would start
the oxidation process.
minium / copper compression cable lugs are the same as those for pure alu- minium versions.
Quality products manufactured by market leaders such as Klauke feature a consistent material thickness, exact diameters and correct fit are a prereq- uisite for ensuring high safety stan- dards are always met. Like aluminium compression cable lugs conforming to DIN 46239, aluminium/copper compres- sion cable lugs feature a barrier design allowing the use of oil soaked and paper insulated cables which prevents oil leakage.
Aluminium conductors at a glance
Aluminium conductors are available in four different versions which require in some cases special processing. These are (see picture 4).
• round solid conductor(re) • sector solid conductor(se) • round stranded conductor (rm) • sector stranded conductor (sm)
These abbreviations will be found next to other markings on all Al/Cu compression cable lugs and identify which conductors will suit the appropri- ate cable lug. (see picture 5).
Markings on the product provide the installer with essential informa-
tions. Marking “16 KL25 150 rm/sm 185 re/se” stands for
• 16: Metric bolt size for connecting bolt – size M16.
• KL: Manufacturer (in this case Klauke)
• 25: Die code • 150: Cross section of conductor
in mm2
• 185: Cross section of conductor in mm2
• re/se: for round single stranded solid and single sector solid conductors
The die code also needs special con- sideration. For an accurate and safe crimp the die reference should be the same as that shown on the cable lug. The die code can be seen on the die face as a mirror image so that after compression the die code is visible on the cable lug for final control and inspection.
For an accurate processing of Al/Cu compression cable lugs it is generally
Picture 3: A professional connection of an aluminium conductor with a copper busbar is done by means of an aluminium cable lug and a copper palm.
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Electroinstallation
recommended to use hexagon crimp- ing dies acc. to DIN 48083 part 4. In order to ensure an accurate and profes- sional crimp avoiding over or under compression is the use of appropriate crimping tools. Poor crimps can result in an increase in joint resistance and tem- peratures that can lead to fires. To pre- vent such issues Klauke solely recom-
mend using the manufacturers crimp- ing tools to crimp their cable lugs.
For instance the special crimping dies for aluminium have a crimp width of 7 mm, i.e. 2 mm wider than the crimping dies for copper cable lugs and connectors. This, however, only applies to 60 kN crimping dies. The reason for this is that dies with a larger crimp width are able to connect a wider con- ductor surface area with the cable lugs and balance the poor conductivity of aluminium. To easily identify which die
should be used, Klauke manufactures aluminium dies in a silver colour while dies for copper are yellow-gold coloured.
Connecting compound for alumi- nium connecting material
All cable lugs and connectors for alu- minium conductors come with a special compound (see picture 6). This aggra- vates the non-conductive oxide layer which is quickly formed on the surface. This compound improves the contact properties and enables a perfect elec- trical connection, and also prevents fur- ther oxygen penetrating the contact joints where further oxidation could take place. To maintain the functional capability of the compound all leading brand cable lugs are sealed with a plas- tic plug to prevent the compound from drying-out and leakage.
Al/Cu Connectors
For a correct connection of aluminium and copper conductors leading manu- facturers such as Klauke offer reduction compression joints with a cross section range from 10 mm2 up to 300 mm2. (see picture 7). These products serve mainly the reconstruction of power lines, i.e. non-tension connections of aluminium conductors acc. to DIN EN 60228 resp. aluminium wires acc. to DIN EN 50182 with copper cables acc. to DIN 48201, part 1 and copper conductors acc. to DIN EN 60228. These compres- sion joints consist of interconnected aluminium (E-Al) and copper parts (acc. to EN 13600).
Normally the aluminium part of the cross section has a much larger diameter (see picture 8) to compen- sate for the poor conductivity of alu- minium. As with the cable lugs here too plastic plugs are used to prevent drying-out and leakage. Important: The use of Al/Cu compression joints requires that the correct processing guidelines for copper and aluminium are observed.
Consequently the aluminium section needs to be crimped like an aluminium compression cable lug (see above). Characteristically for Al/Cu compression joints are the different crimping marks which are 7 mm on the aluminium sec- tion and 5 mm on the copper part for crimping dies up to 60 kN.
Picture 4: Various shapes of aluminium conductors
re – round solid conductor
se – sector solid conductor
rm – round stranded conductor
sm – sector stranded conductor
Picture 5: The markings on the cable lug provide information relating to the crimps, the manu- facturer, cross section and allocation of cable.
Source: Klauke
Picture 6: High quality aluminium cable lugs come with a special compound which improves the contact properties and ensures a perfect electrical connection.
Picture 8: Normally the aluminium section (right) has a larger diameter than the copper section (left) to equalize the poor conductivity of aluminium.
Picture 7: Aluminium and copper conductors with different cross sections are being connected using reduction sleeves.
Non-contact voltage detection in the narrowest spaces – the Greenlee CSJ-100 digital open jaw meter makes it
It is designed for AC current measurements of up to 200 A AC and for AC and DC voltages up to 1000 V. It meets the requirements of safety category IV up to 600 V or
Additional product features are the data-hold-function for recording measurements, the automatic power-off for longer battery life, an audible continuity check and a
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26.01.2009 16:10:45 Uhr
The procedure for the copper sec- tion is absolutely identical as on copper compression cable lugs. The crimping marks on the product give detailed information as to origin and applica- tion of the Al/Cu compression joints. The marking “KL14 50 rm/70 re/se” sig- nifies
• 14: Die code • 50: Cross section of designed
conductor in mm2
• rm/sm: for round stranded and sector stranded conductors
• 70: cross section of solid conductor in mm2
• re/se: for round solid and sector solid conductors
The marks on the copper section also indicate the correct procedure. The standard suggests crimping dies acc. to DIN 48083 part 1, 3 and 4 for solid-, fine and fine stranded conductors; for braided round wires the standard refers to specifications of the manufac- turer. Generally Klauke recommends using hexagon crimping dies acc. to DIN 48083 part 4 for processing the copper section of their compression joints.
Advice: When using crimp connec- tions in the ground it should be strictly observed that the connecting joints should be protected against moisture. (Picture 9). For this application Klauke recommends use of cast-resin joints.
For the application of Al/Cu com- pression joints and cable lugs the fol- lowing should also be considered: These products should not be exposed to bending stresses which could frac- ture the contact point. Application on overhead lines is therefore excluded.
Preview: Crimp profiles at a glance
With a further feature story in one of the next issues of “de” we close the series on cable lugs and connectors. This article will deal with the various crimp profiles which correct selection depends very much on materials and cable types used.
MEHR INFOS
cation?, “de” 1-2/2008, S.33 http://www.de-online.info/archiv/ 2008/08/index.php?Page= elektroinstallation02.html • Cable lugs for special applications,
“de” 8/2008, S.27 http://www.de-online.info/archiv/ 2008/17/index.php?Page= elektroinstallation02.html • Best Practise for Installation of
Aluminium Connectors, „de“ 17/2008, S.26
Book on this issue Schmolke, Herbert: Selection and design of cables and conductors 2007.2, revised and extended edition. 120 pages, paperback, with CD Rom, 18€, ISBN 978-3-8101-0263-8, www.de-online.info/ shop/ fachbuecher/schmolke_kabel.html
Electroinstallation
Picture 9: When used in the ground cast-resin joints protect
the connections against moisture. It is important to consider that the
connection is not subject to bending to avoid the risk of frac-
ture.